The present invention generally relates to the conversion of chemical energy to electrical energy. More particularly, the invention relates to the manufacture of electrode active structures, such as cathode electrodes, for incorporation into electrochemical cells. In building a cathode, particularly one made from a granular material, it is important that the active material is of a uniform thickness and packing density supported on the opposed contact surfaces of the intermediate current collector. Having a uniform layer of active material contacting each side of the current collector promotes improved electrical performance, especially as end-of-life (EOL) cell discharge approaches. Exemplary cathode active materials are silver vanadium oxide (SVO) and fluorinated carbon (CFx).
The present invention is also applicable to anode electrodes, particularly those used in secondary or rechargeable cells where a granular active material is the anode active material. An exemplary anode material is of a granular carbonaceous material.
The present invention is directed to a drop-fill assembly and method for uniformly distributing electrode active particles onto a current collector. The drop-fill assembly comprises a conduit containing two or more spaced apart sifting screens. A funnel is located upstream of the sifting screens to distribute an electrode active powder into the center of the conduit with a downward velocity. The mesh of any one sifting screen is out of direct alignment with respect to the next or previous screen. The electrode active powder is poured into the funnel and distributed across the conduit""s cross-section as it bounces off and passes through the misaligned sifting screens. The powder exits at the bottom of the conduit lying in a thin, uniform layer on a current collector, taking on the shape of the desired electrode due to the boundary of the conduit and pressing fixtures located above and beneath the current collector. A deionizer is typically used to prevent static. The powder layer is then pressed on to the current collector to produce an electrode.
These and other aspects of the present invention will become more apparent to those skilled in the art by reference to the following description and to the appended drawings.